autoload/Powerline: Added aurum:status segment (requires changes to colorscheme to work)
autoload/aurum: Cached reltorepo call
Made aurum#status() use empty string in place of zero
@aurum/drivers/git: Make rf-status() work in statusline

@aurum/drivers/mercurial: Fixed two problems in non-python driver:
1. Repository update was completely wrong, it
duplicated number of changesets
2. It used rev1..rev2 syntax while rev1:rev2 was
needed. Sometimes first is not supported